We present a comprehensive study of the optical and electrical properties of transparent conductive films made from precisely tuned ratios of metallic and semiconducting single-wall carbon nanotubes. The conductivity and transparency of the SWNT films are controlled by an interplay between localized and delocalized carriers, as determined by the SWNT electronic structure, tube-tube junctions, and intentional and unintentional redox dopants. The results suggest that the main resistance in the SWNT thin films is the resistance associated with tube-tube junctions. Redox dopants are found to increase the delocalized carrier density and transmission probability through intertube junctions more effectively for semiconductor-enriched films than for metal-enriched films. As a result, redox-doped semiconductor-enriched films are more conductive than either intrinsic or redox-doped metal-enriched films.

Transparent conducting (TC) films of single-walled carbon nanotubes (SWNTs) have the potential to replace conventional TC oxides in a wide variety of optoelectronic devices. [1][2][3][4][5] TC-SWNT films are particularly attractive for photovoltaics (PV) due to their high transparency over much of the solar spectrum, excellent electrical conductivity, and the potential for inexpensive roll-to-roll processing. SWNT films have been used, by us and others, in cadmium telluride, [6] copper indium gallium diselenide, [7] and organic PV (OPV) devices. [8][9][10] In several reports, SWNTelectrodes for OPV have been prepared by filtering a sodium dodecyl sulfate (SDS)-stabilized dispersion of SWNTs to form a thin film. [9,10] The film can be released by dissolution of the filter, and then transferred to a transparent substrate.[11] This so-called ''transfer method'' produces highly transparent films with excellent conductivity, but the films possess irregular morphologies and significant roughness, which can lead to short-circuits and overall poor reproducibility during device fabrication.[12] Moreover, the process is not scalable. TC-SWNT films have also been produced for optical and electrical studies by air-brush spraying using surfactant-stabilized SWNT inks. Such films are inhomogeneous because SWNTs sprayed from surfactant solutions agglomerate on heated substrates. To move TC-SWNT electrodes beyond the proof-of-concept stage for PV and other optoelectronic applications, methods are required for producing large-area, transparent, conducting SWNT films that are smooth and homogeneous over large areas.Here, we report methods to prepare SWNT films with high transparency, electrical conductivity, and uniformity, with exceptionally low surface roughness, on arbitrarily large (6 inch  6 inch) substrates by ultrasonic spraying. A side-by-side comparison of OPV devices fabricated on SWNT and indiumdoped tin oxide (ITO) electrodes showed very good performance with energy-conversion efficiencies of $3.1 and 3.6%, respectively, under AM 1.5 illumination. Several factors are critical to the success of the approach. First, we prepared aqueous SWNT dispersions using a high-molecular-weight (MW $90 000) polymeric derivative of cellulose (sodium carboxymethyl cellulose (CMC)). CMC has been previously reported as an excellent agent for dispersing SWNTs in water, [13] and transparent films have been drop-cast, [14] but this is the first report of CMC-based dispersions for spraying SWNT films. A second advance is the use of ultrasonic spraying, which, when combined with the CMC-based dispersions, permits precise amounts of SWNTs to be reproducibly and uniformly dispensed over arbitrarily large areas. In fact, by measuring the weight and optical properties of films as a function of the number of deposited layers, the SWNT absorption coefficient could be accurately determined. Finally, we used SWNTs produced by laser vaporization (LV), which have lower defect densities [15,16] than tubes produced by chemical vapor deposition (CVD). Th...

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Nanometer-sized metal particles (e.g., gold and silver) are certain to be important fundamental building blocks of future nanoscale electronic and optical devices. However, there are numerous challenges and questions which must be addressed before nanoparticle technologies can be implemented successfully. For example, basic capping ligand chemistrysnanoparticle electronic function relationships must be addressed in greater detail. New methods for assembling nanoparticles together into higher-order arrays with more complex electronic functions are also required. This review highlights our recent progress toward characterizing electron transport in gold nanoparticles as a function of capping ligand charge state. These studies have shown that single electron tunneling energies can be manipulated predictably via pH-induced charge changes of surfacebound thiol capping ligands. We also show that rigid phenylacetylene molecules are useful bridges for assembling gold and silver nanoparticles into arrays of two, three, and four particles with psuedo D ∞h , D 3h , and T d symmetries. These nanoparticle "molecules" interact electromagnetically in a manner qualitatively consistent with dipole coupling models.

Materials with switchable absorption properties have been widely used for smart window applications to reduce energy consumption and enhance occupant comfort in buildings. In this work, we combine the benefits of smart windows with energy conversion by producing a photovoltaic device with a switchable absorber layer that dynamically responds to sunlight. Upon illumination, photothermal heating switches the absorber layer—composed of a metal halide perovskite-methylamine complex—from a transparent state (68% visible transmittance) to an absorbing, photovoltaic colored state (less than 3% visible transmittance) due to dissociation of methylamine. After cooling, the methylamine complex is re-formed, returning the absorber layer to the transparent state in which the device acts as a window to visible light. The thermodynamics of switching and performance of the device are described. This work validates a photovoltaic window technology that circumvents the fundamental tradeoff between efficient solar conversion and high visible light transmittance that limits conventional semitransparent PV window designs.